Particle range retrieval in heterogeneous phantoms with the prompt gamma ray timing method at a clinical proton accelerator

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potentialities of ion beam therapy. In spite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active-and passively collimated prompt gamma ray imaging systems for range assessment under development in several research centers, the prompt gamma ray timing method has been recently proposed. The transit time of ions through matter correlates to the emission times of prompt gamma rays. Hence, these encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, this method is tested for the first time at a clinical proton accelerator (Westdeutsches Protonen-therapiezentrum Essen, Germany) with heterogeneous phantoms. Different scintillation detectors acquire prompt gamma ray timing distributions at various proton energies. Particle range differences of 2 millimetres in heterogeneous phantoms are identified by visual comparison of the spectrum shape. In conclusion, the prompt gamma ray timing method is feasible for range assessment in a clinical radiation environment, which settles this novel approach as a promising alternative in the field of in vivo dosimetry.